1. Field of the Invention
The present invention relates to a speaker, and more particularly, to a speaker for generating low-frequency sounds which may be used, for instance, as a woofer or other component in a 3D sound system. Furthermore, the present invention relates to a speaker device, and more particularly, to a speaker device including an amplifier and a speaker unit contained in a single case.
2. Description of the Related Art
A bookshelf-type speaker is generally used as a conventional speaker. This speaker includes a dynamic speaker unit provided in a case, and sound is emitted from the front surface of the speaker unit. Sound is generated by the vibrations of a vibrating plate of the speaker unit. The sound generated is emitted not only from the front surface of the vibrating plate but also from a rear side thereof. Since the sound emitted from the front surface of the speaker unit and the sound emitted from the rear side have opposite phases relative to each other, the case in which the speaker is provided cuts off the sound emitted from the rear side of the speaker unit so that the sound waves emitted from the front surface and the sound waves emitted from the rear side do not cancel each other.
However, the sound emitted from the rear side of the speaker unit makes the case vibrate. Such vibration of the case is reduced by using a highly rigid material to construct the case, using reinforcing material to restrict the vibration of the case, and inserting sound-absorbing material inside of the case. As a result, vibration of the case is reduced and the sound emitted from the rear side of the speaker unit is cut off sufficiently, so that only the sound emitted from the front surface of the speaker unit is transmitted to outside of the case.
When this sort of bookshelf speaker is used to manufacture a speaker for generating low-frequency sounds such as a woofer, a large-scale speaker unit is required. Furthermore, to obtain a sufficiently low tone, a large-volume case must be provided. Moreover, since sound emitted from the front surface of the speaker unit is used, the sound obtained has directivity.
As shown in FIG. 12, another conventional audio device relevant to the background of the present invention includes an amplifier provided inside of the case of a speaker. The audio device 1 includes a speaker unit 3 attached to the front surface of a case 2. In addition, a partitioning board 4 is arranged to partition a portion of the inside of the case 2, and an amplifier 5 is attached in the portion partitioned by the partitioning board 4. A through hole 6 is provided in the partitioning board 4, and a distribution hole 6 is provided in the case 2.
In the audio device 1, the amplifier 5 amplifies an input signal and the amplified signal vibrates the vibrator of the speaker unit 3, whereby sound is emitted from the front surface of the speaker unit 3. Further, when the vibrator of the speaker unit 3 vibrates, air inside of the case 2 flows through the through hole 6 in the partitioning board 4 and through the distribution hole of the case 2. This flow of air cools the amplifier 5.
However, since this type of audio device uses sound emitted from the front surface of the speaker unit, the sound which is generated by this audio device has directivity. Furthermore, since the sound emitted from the rear side of the speaker is opposite in phase to the sound emitted from the front surface of the speaker unit, it is necessary to prevent these sounds from cancelling each other. Consequently, it is necessary to cut off sound emitted from the rear side of the speaker unit, and to restrict vibration of the case by reinforcing the case, inserting sound-absorbing material, and taking other corrective measures. More specifically, a speaker for producing low-frequency tones, such as a woofer, has a large speaker unit and therefore requires a large-volume case. When such a large case is used, and an amplifier is provided inside of the case, the large size of the speaker and the corresponding large volume of the case make it difficult to reduce the size of the whole structure.
In order to overcome the problems described above, preferred embodiments of the present invention provide a speaker and a speaker device which have a greatly reduced size and emit sound waves in a non-directional manner.
A speaker according to preferred embodiments of the present invention includes a speaker unit and a case attached to the speaker unit, and the speaker unit being arranged to emit sounds to outside of the case as a result of the case vibrating in response to vibration of the speaker unit.
In such a speaker, the speaker unit is arranged inside of the case so that when the case is mounted on a support or mounting surface, the speaker unit faces toward the support or mounting surface on which the case is supported or installed.
Preferably, a space inside of the case defined by the speaker unit and the inner surfaces of the case, is airtight.
In addition, a port may be provided on the bottom surface of the case located at the surface closest to the location of the support or mounting surface.
Preferably, the inner portion of the case does not have a structure which would restrict the vibration of the case.
The back-and-forth vibration of the vibrator of the speaker unit causes the case to vibrate in an expanding and contracting motion. As a result of this expansion and contraction of the case, non-directional spherical waves are emitted to areas outside of the case. The expansion and contraction of the case caused by the back-and-forth vibration of the speaker unit is generated when pressure, created by the vibration of the speaker unit, is transmitted to the air inside of the case, whereby the pressure is transferred to the case. Therefore, in order to make the case expand and contract effectively, the case should preferably have small volume, enabling the speaker to have a very small size.
Preferably, the speaker unit faces the airtight space inside of the case in order to make the case expand and contract effectively. By storing the speaker unit inside of a very small case, the resonant frequency of the speaker is significantly increased, enabling the fidelity of the speaker to be improved by generating sound at frequencies below the resonant frequency.
By providing the speaker unit on a floor side of the case, it is possible to cut off sound emitted from the speaker unit to the outside thereof, so that only sound generated by the expansion and contraction of the case is emitted.
Furthermore, a port may be provided at the bottom portion of the case to accentuate low-frequency tones, so that the low-frequency sound emitted from the speaker unit toward the floor exits through the port.
A speaker device according to a preferred embodiment of the present invention includes a case, an amplifier main body stored inside of the case, and a speaker unit stored inside the case, the amplifier main body being provided in front of the speaker unit.
In such a speaker device, the amplifier main body is provided on the support or mounting surface side of the case, and the speaker unit is arranged so as to face toward the installation surface and so as to emit sound through the amplifier main body.
Furthermore, a gap may be provided between the inner wall of the case and the amplifier main body. As a result of this arrangement, the vibrations of the speaker unit send air through the gap, thereby cooling the amplifier main body. In addition, the gap is used as a load horn which makes is arranged to cause sound emitted from the speaker unit to pass through the load horn.
Furthermore, the case vibrates by being vibrated by vibration of the speaker unit, thereby emitting sound to the outside of the case due vibration of the case.
It is preferable that the inner portion of the case does not have a structure which would restrict the expansion and contraction of the case.
Inside of the case, the amplifier main body is preferably provided in front of the speaker unit, so that sound emitted from the front surface of the speaker unit is emitted into the space where the amplifier main body is provided. At this point, the weight of the amplifier main body restricts unwanted vibrations, preventing the sound from reaching to the outside of the case. Then, sound emitted from the rear side of the speaker unit expands and contracts the case, and the expansion and contraction of the case emits sound to the outside of the case. The expansion and contraction of the case is excited when pressure, generated by the vibration of the speaker unit, is transmitted to the air inside of the case, whereby the pressure is transferred to the case. Therefore, in order to make the case expand and contract effectively, the case should preferably have very small volume, thereby enabling the speaker to have a very small size.
Thus, by utilizing the expansion and contraction of the case, caused by the vibration of the speaker unit, the overall size of the speaker is significantly reduced. Consequently, even when the amplifier has a small case, a speaker including the speaker unit and the amplifier case can be obtained by expanding and contracting the case using the vibration of the speaker unit.
In this type of speaker device, the speaker unit is preferably arranged so that it faces toward the floor or mounting surface so as to use the expansion and contraction of the case. That is, the case of the speaker device is provided so that the amplifier faces the floor or mounting surface and is located closest to floor or mounting surface as compared to the speaker unit.
Furthermore, when a gap is provided between the inner walls of the case and the amplifier main body, the vibration of the speaker unit forces air through the gap, and this flow of air cools the amplifier main body. In addition, sound emitted from the front surface of the speaker unit passes through the gap, which thereby functions as a load horn to accentuate the low tones.
These and other objects, features and advantages of the present invention will become clearer when the following detailed description of preferred embodiments is read in conjunction with the accompanying drawings.